Positronium chemistry by quantum Monte Carlo. I. Positronium-first row atom complexes

The stability of the ground and excited states of Positronium-atom complexes [A, Ps], Ps = [e+,e-], has been explored for A=Li, B, C, O, F using variational and diffusion Monte Carlo techniques. From the numerical results of our simulations it turns out that the ground state of the complexes [Li, Ps]2S, [C, Ps]3S, [O, Ps]1P, and [F, Ps]2S is stable against the break up in the two neutral fragments A and Ps, while the ground state of [B, Ps]2P has an energy above the same dissociation threshold. As to the excited states, the only possible candidate, [F, Ps]2P, has a total energy statistically equal to the lower dissociation threshold, i.e. it does not seem to be stable against the dissociation.